Recently, silicon carbide semiconductors have attracted a lot of attention as a new type of semiconductor materials. Silicon carbide semiconductors have a greater dielectric breakdown voltage, a higher electron saturated drift velocity, and a higher thermal conductivity than silicon semiconductors. For that reason, researches and developments have been carried on extensively to realize, using those silicon carbide semiconductors, power devices which can operate at higher temperatures, at higher speeds and with a larger amount of current supplied than conventional silicon devices. Among other things, since motors for use in electric motorcycles, electric cars and hybrid cars are either AC driven or inverter-controlled, development of high-efficiency switching elements for use in those applications is awaited by many people. To realize such a power device, a single-crystal silicon carbide wafer is needed to grow epitaxially a silicon carbide semiconductor layer of quality thereon.
A single crystal semiconductor wafer is generally obtained by slicing a block of a single-crystal semiconductor material which is called either an “ingot” or a “rod” with a multi-wire saw (see Patent Document No. 1, for example).